---
title: ISO and Broadcast Calendars
sidebar_position: 3
---

DayPicker can follow different week numbering systems. You can switch to ISO 8601 week numbering or to the US broadcast calendar, which both override the default week rules from the current locale.

Use only one of these systems at a time: `ISOWeek` or `broadcastCalendar`.

## ISO 8601 calendar

Use the `ISOWeek` prop to switch to [ISO week dates](https://en.wikipedia.org/wiki/ISO_week_date). With ISO 8601:

- Weeks always start on Monday.
- Week 1 is the week that contains the first Thursday of the year.
- Week numbers follow the ISO standard instead of locale-specific rules.

| Prop Name | Type      | Description                                                            |
| --------- | --------- | ---------------------------------------------------------------------- |
| `ISOWeek` | `boolean` | Use ISO 8601 week rules (weeks start on Monday, ISO-compliant week 1). |

```tsx
<DayPicker ISOWeek showWeekNumber />
```

<BrowserWindow>
  <Examples.WeeknumberIso />
</BrowserWindow>

## Broadcast calendar

Use the `broadcastCalendar` prop to switch to the US broadcast calendar, commonly used in the TV and radio industry. In this system:

- Weeks start on Monday.
- Week 1 starts with the first Monday of the calendar year.
- Months are displayed as 4 or 5 complete broadcast weeks.

| Prop Name           | Type      | Description                                                                |
| ------------------- | --------- | -------------------------------------------------------------------------- |
| `broadcastCalendar` | `boolean` | Use the US broadcast calendar (weeks start Monday, week 1 = first Monday). |

```tsx
<DayPicker broadcastCalendar showWeekNumber />
```

<BrowserWindow>
  <Examples.BroadcastCalendar />
</BrowserWindow>
